Email Metrics That Matter for Small Teams

The Metric Trap Small Teams Fall Into

You send an email campaign. Your inbox explodes with numbers: open rate, click-through rate, bounce rate, unsubscribe rate, conversion rate, revenue per email, list growth rate. Your email platform throws a dashboard at you with fifteen different charts. You stare at them. Some are green. Some are red. You have no idea what to do next.

This is the metric trap, and small teams get stuck in it constantly.

The problem isn’t that you’re lazy or that you don’t understand analytics. The problem is that most email platforms were built for enterprise teams with dedicated analytics specialists, data engineers, and revenue operations managers. They show you everything because they can afford to have someone make sense of it all.

You can’t. You have one person running marketing, or maybe two. You need to know which metrics actually move the needle for your business and which ones are just noise.

This guide cuts through the fog. We’ll walk through the metrics that genuinely predict growth for small teams, show you how to measure them, and tell you which ones you can safely ignore. We’ll also show you how tools like Mailable can help you focus on the metrics that matter by automating the execution side—so you spend less time building emails and more time analyzing what works.

Why Most Email Metrics Mislead You

Before we talk about which metrics matter, let’s understand why so many metrics don’t.

Open rate is the classic example. For years, marketers obsessed over open rates like they were the holy grail of email performance. “We got a 28% open rate!” they’d announce proudly. The problem: open rates are almost completely out of your control, and they don’t correlate strongly with business outcomes.

Open rates depend on subject line, sender name, send time, and the recipient’s email client. They’re influenced by whether someone’s on mobile or desktop, whether they use Apple Mail Privacy Protection (which inflates opens), and whether they even opened the email or just previewed it. None of that tells you if the email actually moved someone toward a purchase or signup.

The same applies to bounce rates, unsubscribe rates, and a dozen other vanity metrics. They feel important because they’re easy to measure and they show up on your dashboard. But they don’t tell you if your email is making money.

Small teams need metrics tied directly to outcomes: revenue, signups, retention, or whatever your core business metric is. Everything else is supporting data.

According to research on email marketing metrics, many marketers track metrics that don’t correlate with revenue. The guide emphasizes that small teams should focus on metrics that drive business results rather than vanity metrics that look good on a dashboard.

The Three Categories of Email Metrics

Let’s organize this. Email metrics fall into three buckets:

1. Execution Metrics — Did your email get delivered and opened? (Deliverability, open rate, click rate.)

2. Engagement Metrics — Did people interact with your email in meaningful ways? (Time spent, link clicks, reply rate.)

3. Business Metrics — Did the email drive revenue, signups, or retention? (Conversion rate, revenue per email, customer lifetime value lift.)

Most small teams obsess over execution metrics because they’re easy to measure. But execution metrics are hygiene factors. You need them to work, but they don’t tell you if anything matters.

Engagement metrics are more useful. They start to show you which messages resonate. But they still don’t close the loop on whether an email actually drove a business outcome.

Business metrics are what you should optimize for. They’re harder to measure because they require connecting email data to your CRM, payment system, or analytics platform. But they’re the only ones that matter.

Deliverability: The Non-Negotiable Foundation

Let’s start with the one metric you absolutely have to get right: deliverability.

Deliverability is simple: what percentage of your emails actually made it to the inbox? Not spam folder. Not bounced. Inbox.

Your deliverability target should be 98% or higher. Below that, something is broken. It could be your list quality, your sending infrastructure, your domain reputation, or your authentication setup (SPF, DKIM, DMARC).

How do you measure it? Most email platforms calculate it automatically. But the real test is to check your bounce rate and complaints. If your bounce rate is above 2%, your list has problems. If your complaint rate is above 0.1%, your content is hitting spam filters or people are marking you as spam.

Why does this matter? Because everything downstream depends on deliverability. You could have the most brilliant email ever written, but if it lands in spam, it doesn’t matter. Deliverability is table stakes.

The good news: for most small teams using reputable email infrastructure, deliverability is solved. You don’t need to obsess over it. Just make sure you’re not buying email lists, you’re authenticating your domain properly, and you’re honoring unsubscribes and bounces.

Click-Through Rate: The One Execution Metric That Matters

Open rate is a trap. Forget about it.

Click-through rate (CTR) is different. It’s a real signal.

CTR is the percentage of people who received your email that clicked on a link. It’s much harder to fake than open rate. Someone has to actually engage with your email content and decide to click. That’s a meaningful action.

For small teams, CTR is your leading indicator for engagement. If your CTR is low, something’s wrong with your email: the copy isn’t compelling, the offer isn’t clear, the link isn’t prominent, or you’re emailing the wrong people.

What’s a good CTR? It depends on your industry and audience. Industry benchmarks for email metrics show that average CTR ranges from 1% to 5% depending on the type of email and industry. But for small teams, you should aim higher. If you’re sending targeted, relevant emails to an engaged list, 5-10% CTR is reasonable. If you’re consistently below 2%, something’s off.

How to improve CTR:

• Make the CTA obvious. One clear call-to-action per email. Don’t bury it in a wall of text.
• Write copy that creates curiosity or urgency. “Learn how to 3x your email CTR” is more compelling than “Read our blog post.”
• Test different CTAs. Subject lines, copy length, button text, button color. A/B test ruthlessly.
• Segment your list. Sending the same email to everyone kills CTR. Send different emails to different segments.

CTR is also something you can improve with tools like Mailable, which generates production-ready email templates optimized for engagement. Instead of spending hours designing emails or writing copy, you describe what you want in plain English, and Mailable builds it for you. That frees you up to focus on the metrics that matter.

Conversion Rate: Where Email Meets Revenue

Now we’re getting to the metrics that matter.

Conversion rate is the percentage of people who received your email that completed a desired action: made a purchase, signed up, downloaded something, booked a call, whatever your goal is.

This is the bridge between email and business outcomes. If your conversion rate is 2%, that means for every 100 people you email, 2 take the action you want.

Conversion rate is harder to measure than open rate or click rate because it requires connecting your email platform to your website analytics, CRM, or payment system. But it’s worth the effort.

How to measure it:

1. Use UTM parameters. Add tracking parameters to your email links so you can identify traffic from email in Google Analytics or your analytics platform. Example: https://yoursite.com/product?utm_source=email&utm_campaign=summer_sale

2. Use email platform integrations. Most modern email platforms integrate with Shopify, Stripe, or your CRM. They can track conversions automatically.

3. Set up conversion pixels. Add tracking code to your “thank you” page so you can attribute conversions back to the email.

Once you have conversion data, you can optimize. What emails convert best? What segments convert best? What time of day gets the highest conversion rate? These are the questions that move the needle.

For most small teams, a 1-3% conversion rate on promotional emails is solid. For lifecycle or transactional emails, it should be higher (5-15%), because those are already engaged users.

Revenue Per Email: The True North Metric

If conversion rate is the bridge, revenue per email is the destination.

Revenue per email is simple: total revenue generated by an email divided by the number of emails sent.

Example: You send 10,000 emails. 200 people click through. 50 people buy. Average order value is $50. Total revenue is $2,500. Revenue per email is $0.25.

This is the metric that matters most for small teams because it directly ties email to money. It’s also the metric that helps you decide what’s worth doing.

If you’re spending 2 hours writing and designing an email, and it generates $0.25 per email, and you’re sending to 5,000 people, that’s $1,250 in revenue for 2 hours of work. That’s a good use of time.

If you’re spending 2 hours on an email that generates $0.05 per email, that’s $250 in revenue. Maybe that’s not worth your time.

Revenue per email also helps you optimize your email strategy. Which types of emails have the highest revenue per email? Which segments? Which products? Once you know, you can focus on what works.

The challenge with revenue per email is attribution. If someone receives 5 emails over a month and then buys, which email gets credit? This is why understanding email marketing metrics requires connecting your email platform to your revenue system.

Most email platforms don’t make this easy. They show you clicks and opens, but connecting that to revenue requires manual work or custom integrations. This is one area where small teams often struggle.

The fix: use your CRM or analytics platform as the source of truth. Track which emails drive which conversions, and calculate revenue per email from there. It’s more work upfront, but it’s the only way to know what’s actually working.

Customer Acquisition Cost (CAC): The Unit Economics

Here’s a metric that ties everything together: customer acquisition cost.

CAC is the total cost of acquiring a customer divided by the number of customers acquired. For email, it’s the cost of your email platform, plus your time, divided by the number of new customers you acquired through email.

Example: You pay $100/month for email software. You spend 10 hours per month on email (at $50/hour = $500). That’s $600/month in email costs. You acquire 20 new customers through email in a month. Your CAC is $30 per customer.

Why does this matter? Because it tells you if email is an efficient way to acquire customers.

If your average customer lifetime value (LTV) is $500, and your CAC is $30, you have a 16:1 LTV:CAC ratio. That’s fantastic. You can spend more on email and still be profitable.

If your LTV is $100 and your CAC is $30, you have a 3:1 ratio. That’s okay, but you need to be careful about scaling.

If your LTV is $50 and your CAC is $30, you have a 1.6:1 ratio. That’s not sustainable. You need to either improve your email conversion rate, increase customer lifetime value, or reduce email costs.

CAC forces you to think about email as a business function, not a marketing tactic. It connects email to unit economics, which is how small teams should think about all their channels.

To calculate CAC, you need:

• Total email costs (platform, time, content creation, design)
• Total customers acquired through email (tracked via UTM parameters or CRM attribution)
• Time period (usually monthly or quarterly)

Once you have this, you can compare email CAC to other channels (paid ads, content, partnerships, sales). If email has the lowest CAC, double down on it. If it’s the highest, rethink your strategy.

Retention and Churn: The Metrics Nobody Tracks But Should

Here’s the dirty secret: most small teams obsess over acquiring new customers and completely ignore retention.

Retention is the percentage of customers who stay customers over a given period. Churn is the opposite: the percentage who leave.

For email, retention metrics tell you if your lifecycle emails are working. Are you keeping customers engaged after they buy? Are you reducing churn?

Retention is massively underrated because it’s hard to measure and it takes time to see results. But it’s often 5-10x cheaper to retain a customer than acquire one.

How to measure retention:

1. Calculate churn rate. For a given month, take the number of customers you started with, subtract the number who left, and divide by the starting number. Example: You start with 100 customers. 5 leave. Churn rate is 5%.

2. Track repeat purchase rate. For e-commerce, what percentage of customers buy more than once? What’s the time between purchases?

3. Track engagement over time. For SaaS or subscription businesses, track how often customers log in or use key features.

4. Measure email engagement by cohort. Segment your email list by when they became customers (cohorts), and track how their engagement changes over time. New customers should be more engaged than old customers. If engagement drops sharply, you have a retention problem.

Once you have retention data, you can use email to improve it. Send re-engagement emails to inactive customers. Send product tips to new customers. Send win-back emails to churned customers. These lifecycle emails are some of the highest-ROI emails you can send.

The reason most small teams don’t track retention is because it requires connecting email to your CRM or analytics platform. It’s not a one-click dashboard metric. But it’s worth the effort.

List Growth Rate: The Vanity Metric That Matters

List growth rate is the percentage growth of your email list over a given period.

Example: You start the month with 10,000 subscribers. You end with 11,000. That’s 10% growth.

List growth rate is a vanity metric in the sense that it doesn’t directly tell you if email is working. You could grow your list by 100% but have terrible engagement and conversion.

But list growth rate does matter because it’s a leading indicator. A growing list means you’re adding engaged, interested people. A shrinking list means you’re losing people faster than you’re adding them.

For small teams, list growth should be a secondary priority. Your first priority is making sure your current list is engaged and converting. But once you have that working, growing your list amplifies the impact.

How to grow your list:

• Add signup forms to your website. Pop-ups, embedded forms, exit-intent forms.
• Offer an incentive. A free guide, discount code, or exclusive content in exchange for email.
• Promote signup on social media. Link to your signup page from Twitter, LinkedIn, etc.
• Add signup to your checkout flow. For e-commerce, ask for email on the checkout page.
• Partner with other businesses. Co-marketing campaigns, guest posts, podcast appearances.

List growth rate is also influenced by your unsubscribe rate. If you’re growing your list at 5% per month but losing 3% per month to unsubscribes, your net growth is only 2%. That’s why segmentation and relevance matter. If you’re only emailing people about topics they care about, your unsubscribe rate stays low.

Email Frequency and Engagement Decay

Here’s a metric that’s not usually tracked but should be: engagement decay.

Engagement decay is the natural decline in email engagement over time. You send an email. Some people open it and click. You send another email a few days later. Fewer people open it. You send another email a week later. Even fewer people open it.

This is normal. People get busy. They lose interest. Their inbox fills up. Engagement naturally decays.

The question for small teams is: what’s your optimal email frequency?

If you email too infrequently, people forget who you are. If you email too frequently, people unsubscribe.

The sweet spot depends on your audience and content. A SaaS company might email daily (product updates, tips). An e-commerce company might email weekly (sales, new products). A newsletter might email monthly.

How to find your optimal frequency:

1. Track engagement by email frequency. Segment your list into different frequency groups. Send one group emails 2x per week, another 1x per week, another 2x per month. Track which group has the highest engagement and conversion rate.

2. Monitor unsubscribe rate by frequency. As you increase frequency, your unsubscribe rate will increase. Find the point where the additional revenue from more emails is offset by the cost of losing subscribers.

3. Watch for engagement decay. If you’re emailing the same people multiple times per week, track their engagement over time. Do they stay engaged, or does engagement drop sharply?

For most small teams, 1-2 emails per week is a good starting point. But test it with your audience.

This is where tools like Mailable help. Instead of manually creating each email, you can generate sequences and drip campaigns from a prompt. That makes it easier to test different frequencies and see what works.

Segmentation and Relevance: The Hidden Leverage Point

Here’s a metric that’s not usually tracked but should be: relevance.

Relevance is how well your email matches the recipient’s interests and needs. It’s not a single metric, but it’s the biggest lever for improving all other metrics.

When you segment your list and send targeted emails, everything improves:

• Open rate goes up. Because the subject line is relevant to the recipient.
• Click rate goes up. Because the content is relevant.
• Conversion rate goes up. Because you’re offering something the person actually wants.
• Unsubscribe rate goes down. Because you’re not sending irrelevant emails.
• Revenue per email goes up. Because more people are interested in what you’re offering.

How to measure relevance:

1. Track metrics by segment. Create segments based on behavior (past purchases, pages visited), demographics (industry, company size), or engagement (active, inactive). Send different emails to different segments. Compare the metrics.

2. Calculate segment-level conversion rate. Which segments convert best? Which segments have the highest revenue per email?

3. Track segment engagement decay. Do certain segments disengage faster than others?

Once you have this data, you can optimize. Double down on segments with high engagement and conversion. Rethink your approach for segments with low engagement.

Segmentation requires work. You need to categorize your subscribers, create different email versions, and track segment-level metrics. But it’s one of the highest-ROI activities for small teams.

Tools like Mailable make segmentation easier. You can generate different email templates for different segments from a single prompt. Instead of manually creating 5 versions of an email, you generate them in seconds.

A/B Testing: The Compounding Advantage

A/B testing is the process of sending two versions of an email (version A and version B) to a small portion of your list, measuring which performs better, and sending the winning version to the rest of your list.

A/B testing isn’t a metric, but it’s how you improve metrics.

For small teams, A/B testing is one of the highest-ROI activities because the cost is low and the upside is high. You can test:

• Subject lines. Does “[Name], your order is ready” outperform “Your order is ready”?
• Send time. Do people open more emails at 9am or 2pm?
• Copy length. Do short emails outperform long emails?
• CTA text. Does “Buy now” outperform “Claim your discount”?
• Sender name. Does email from “Founder” outperform email from “Sales”?

Each test that wins compounds. If you test 10 variables and each one improves your conversion rate by 10%, your total conversion rate improves by 100% (2.59x, to be exact).

How to run A/B tests:

1. Pick one variable. Only test one thing at a time. If you test subject line and send time simultaneously, you won’t know which one caused the improvement.

2. Split your list. Send version A to 50% of your list, version B to the other 50%. Wait long enough for people to open and click (usually 24-48 hours).

3. Choose a winner. Which version had higher click rate or conversion rate? Send that version to the remaining subscribers who didn’t receive either version.

4. Document the result. Keep a log of what you tested and what won. Over time, you’ll see patterns.

5. Test the next variable. Once you have a winning subject line, test send time. Once you have a winning send time, test copy length.

Small teams often skip A/B testing because it takes time to set up. But if you’re sending emails anyway, you might as well test. The marginal cost is zero.

Actionable Metrics Dashboard for Small Teams

Let’s bring this together. If you’re a small team, here’s what you should actually track:

Daily/Weekly Metrics:

• Deliverability rate (should be 98%+)
• Bounce rate (should be <2%)
• Click-through rate (target depends on email type, but 2-10% is reasonable)

Monthly Metrics:

• Conversion rate (by email, by segment, by funnel stage)
• Revenue per email (by email, by segment)
• List growth rate (signups minus unsubscribes)
• Unsubscribe rate (should be <0.5%)

Quarterly Metrics:

• Customer acquisition cost (email channel)
• Lifetime value of customers acquired through email
• Retention rate (by cohort, by segment)
• Email engagement by cohort (how does engagement change over time?)

Ongoing:

• A/B test results (keep a log)
• Segment-level metrics (compare performance across segments)
• Relevance improvements (are you sending more targeted emails?)

That’s it. You don’t need fifteen metrics. You need these ten, tracked consistently, and connected to your business outcomes.

The mistake most small teams make is tracking everything and understanding nothing. Track fewer metrics, understand them deeply, and act on them.

How to Connect Email Metrics to Your Systems

Tracking metrics is one thing. Connecting them to your revenue system is another.

Here’s the infrastructure you need:

1. Email platform with good API and integrations. You need to be able to track which email drove which conversion. Mailable provides API, MCP, and headless support, which means you can connect it to your CRM, analytics platform, or custom system.

2. UTM parameter discipline. Every link in every email should have UTM parameters so you can track traffic and conversions in Google Analytics.

3. CRM or analytics platform that connects to your email. Shopify, Stripe, HubSpot, Mixpanel—something that lets you see which emails drove which customers.

4. A spreadsheet or dashboard to track metrics over time. Most email platforms show you metrics for individual campaigns, but you need a place to track trends. Google Sheets works fine.

Once you have this infrastructure, measuring metrics becomes automatic. You send an email, it generates clicks and conversions, those conversions are attributed back to the email, and you can see the revenue impact.

The reason most small teams don’t do this is because it requires work upfront. But it’s worth it. Once it’s set up, you have visibility into what’s actually working.

The Metrics to Ignore (Or Ignore Most of the Time)

Let’s be explicit about what to ignore:

Ignore open rate. It’s not actionable and it’s influenced by too many factors outside your control. Apple Mail Privacy Protection inflates open rates for Apple users. Some email clients auto-open emails. Some people open emails multiple times. Open rate is noise.

Ignore complaint rate unless it’s high. A complaint rate above 0.1% is a problem. Below that, ignore it. It’s not predictive of anything.

Ignore list size. A list of 100,000 disengaged subscribers is worth less than a list of 1,000 engaged subscribers. Focus on engagement and conversion, not list size.

Ignore industry benchmarks unless you’re stuck. Your open rate is irrelevant compared to industry average. Your conversion rate compared to your own historical average is relevant. Track your own metrics, not benchmarks.

Ignore vanity metrics. Shares, forwards, social media mentions—they feel good but they don’t predict revenue. Focus on clicks and conversions.

The reason to ignore these metrics is simple: they distract you from what matters. Every minute you spend analyzing open rate is a minute you’re not spending on improving conversion rate or customer retention.

Building a Metrics-Driven Email Culture

Here’s the thing about metrics: they only matter if you act on them.

Small teams often track metrics, see that something’s not working, and then continue doing the same thing. That defeats the purpose.

To build a metrics-driven email culture:

1. Set targets. What conversion rate are you aiming for? What revenue per email? What customer acquisition cost? Write it down.

2. Review metrics weekly. Spend 30 minutes every week looking at the previous week’s metrics. What worked? What didn’t? What should you test next week?

3. Run A/B tests continuously. Pick one variable to test each week. Over a month, you’ll have 4 tests. Over a year, you’ll have 52 tests. The compounding effect is massive.

4. Share metrics with your team. If you have a team, make sure everyone sees the metrics. It keeps everyone focused on outcomes.

5. Connect metrics to revenue. Every week, calculate how much revenue your emails generated. This keeps you motivated and it justifies the time you spend on email.

6. Iterate based on data. If a segment has low conversion rate, send different emails to that segment. If a send time underperforms, test a different send time. Let data drive decisions.

Metrics are only useful if they lead to action. Mailable helps with the action part by making it fast to generate and test new emails. Instead of spending hours designing emails, you generate them from a prompt and send them out. That frees you up to focus on metrics and optimization.

Tools and Integrations for Tracking Metrics

You don’t need fancy tools to track metrics. But a few integrations make it easier.

Email platform: You need something that tracks clicks, conversions, and revenue. Mailable integrates with your CRM and analytics platform via API, so you can track everything in one place.

Analytics platform: Google Analytics is free and works well. Set up UTM parameters in your emails and you can see exactly which emails drove traffic and conversions.

CRM: HubSpot, Pipedrive, or whatever you use to track customers. Connect it to your email platform so you can see which emails drove which deals.

Spreadsheet or dashboard: Google Sheets, Airtable, or a custom dashboard. Use this to track metrics over time and spot trends.

Automation platform: If you’re running sequences or drip campaigns, you want something that automates the execution. Mailable can generate entire sequences from a prompt, which means you can set it and forget it while you focus on metrics.

The key is integration. You want your email platform, analytics platform, and CRM talking to each other. That way, you see the full picture: email sent → click → conversion → revenue.

Real-World Example: Small E-Commerce Team

Let’s walk through a real example. Imagine you’re running email for a small e-commerce brand. You have 15,000 subscribers. You send 2 emails per week. You want to know if email is working.

Week 1: You send a promotional email about a summer sale. 15,000 emails sent. 2,100 opens (14% open rate). 315 clicks (2.1% click-through rate). 32 purchases (10% of clicks convert). $1,600 in revenue (average order value $50).

Your revenue per email is $1,600 / 15,000 = $0.107 per email.

Your conversion rate is 32 / 15,000 = 0.21%.

Now, here’s the question: is this good?

You don’t know yet because you don’t have historical data. So you run the same email next week and compare.

Week 2: You send the same email to a different segment (people who haven’t purchased in 30 days). 8,000 emails sent. 960 opens (12% open rate). 96 clicks (1.2% click-through rate). 5 purchases (5% of clicks convert). $250 in revenue.

Revenue per email: $250 / 8,000 = $0.031 per email.

Conversion rate: 5 / 8,000 = 0.06%.

This segment is way less responsive. Maybe they’re not interested in the summer sale. Or maybe they need a different message.

So you test. Week 3: You send a different email to that segment—a “we miss you” email with a 20% discount. 8,000 emails sent. 800 opens (10% open rate). 120 clicks (1.5% click-through rate). 18 purchases (15% of clicks convert). $900 in revenue.

Revenue per email: $900 / 8,000 = $0.1125 per email.

Conversion rate: 18 / 8,000 = 0.225%.

Much better. The “we miss you” email works better for inactive customers than the summer sale email.

So you keep sending the “we miss you” email to inactive customers and the summer sale email to active customers. You’re now optimizing based on data.

Over a year, small optimizations like this compound. If you improve your revenue per email by 10% every quarter, you’re up 46% by year-end. Same list size, same email frequency, but 46% more revenue.

That’s the power of metrics-driven email.

Conclusion: Focus on What Moves the Needle

Email metrics can be overwhelming. But they don’t have to be.

For small teams, focus on three things:

1. Deliverability. Make sure your emails actually reach the inbox.
2. Engagement. Track click-through rate and conversion rate. These tell you if people care about your emails.
3. Revenue. Connect email to your business outcomes. Revenue per email, customer acquisition cost, retention lift—these are what matter.

Ignore open rate, ignore list size, ignore benchmarks. Track your own metrics, test continuously, and let data drive decisions.

Tools like Mailable make this easier by automating the email creation side. You describe what you want, it generates production-ready templates and sequences, and you can focus on measuring what works instead of building emails from scratch.

Start with the metrics we outlined. Track them for a month. Find patterns. Test improvements. Measure the impact. Repeat.

That’s how small teams build email programs that actually move revenue.

For more detailed guidance on email metrics, check out HubSpot’s comprehensive guide to email marketing metrics, Shopify’s breakdown of critical email metrics for small businesses, and Litmus’s strategic framework for measuring email performance. These resources dive deeper into specific metrics and implementation strategies.

If you want to focus more on optimization and less on email creation, Mailable can help. Generate email templates, sequences, and sales funnels from a prompt. API, MCP, and headless support mean you can integrate it into your existing workflows. Then spend your time on metrics and testing instead of design and copy.

The metrics that matter are the ones that move your business forward. Everything else is noise.