Signal vs Hamming
Hamming stress-tests voice agents and monitors health. Signal reads your Retell flow and calls and tells you which step to fix.
In short
Hamming is test-first: it generates scenarios from your prompt, runs large volumes of simulated calls, red-teams the agent, and monitors production health, turning a failed production call into a regression test. Signal reads your Retell agent's flow and production calls, places each repeated failure on a step with a cause, and tells you whether a new version made things better for real callers. Hamming tells you whether the agent is healthy and keeps failures from coming back. Signal tells you what to change. Hamming's docs are gated and its prices are not published, so this page is built from their public marketing pages and FAQ.
Side by side
- Main job
- HammingSimulate, red team and monitor
- SignalFind what to fix in production and check that the fix worked
- Started from
- HammingPre-launch testing
- SignalUnderstanding production calls
- Retell connection
- HammingYou forward Retell's call_ended payload to their API
- SignalAPI key; reads config and calls over the API; no webhook
- Agent config read
- HammingThe prompt, to generate tests
- SignalFull flow: steps, transitions, tools, versions
- A call is graded against
- Hamming50+ built-in scorers plus custom assertions
- SignalA one-page brief you approve; outcomes from platform facts first
- Outcomes
- HammingOutcome tags such as outcome:failure:authentication_failed
- SignalA fixed list of bad outcomes, each with a cause or 'cause not established'
- Issue placed on a flow step
- HammingNot in public material
- SignalYes
- Configured flow vs what production did
- HammingNot in public material
- SignalYes, your flow with production traffic on it
- Version comparison
- HammingRegression suites per release
- SignalBefore and after on production calls, with a verdict only when the difference is real
- Production failure to test
- HammingYes, one click, runs on every release
- SignalTests built from stored production calls
- Simulation
- HammingYes: 50K+ concurrent, accents, noise, 65 languages
- SignalReplays of your stored production calls only
- Red teaming
- HammingYes
- SignalNo
- Compliance
- HammingSOC 2 Type II, HIPAA BAA
- SignalNone. PII handled, no PHI
- How they bill
- HammingQuote only; volume based (tests plus monitored calls); no self-serve trial
- SignalFlat monthly plans with one credit balance; no charge per metric; no overage
Choose Hamming if
- You need large-scale simulated testing before release (Hamming advertises 50,000+ concurrent test calls, accents, noise and IVR trees).
- You need red teaming: prompt injection, jailbreaks and PII leakage, each turned into a failing test.
- You need SOC 2 Type II or a HIPAA BAA, or you work in healthcare.
- You want a failed production call turned into a regression test in one click.
- You want OpenTelemetry traces across speech to text, model and text to speech, with p50, p90 and p99 latency.
- You test in many languages (Hamming lists 65).
Choose Signal if
- You want to sign up and see your own board today, with published prices.
- You want each issue placed on the step of your flow where it happens, with a cause.
- You want 'the fix worked' checked on production calls, with a verdict only when the difference is real.
- You do not want to set up a webhook relay: Signal reads your calls over the Retell API.
- You do not want to write assertions or pick scorers before you know what is wrong.
What the same calls cost across the market
Every vendor at its list price for the same customer at 1,000, 10,000 and 50,000 calls a month: 3-minute calls, one seat, monitoring only, no simulation.
| Vendor | 1,000 calls | 10,000 calls | 50,000 calls |
|---|---|---|---|
| Signal, monthly | $49Starter, $0.049 a call | $499Scale, $0.050 a call | from $1,500Enterprise, $0.030 a call |
| Signal, annual | $39Starter, $0.039 a call | $425Scale, $0.043 a call | CustomEnterprise |
| Tuner | $39Builder, $0.039 a call | $376.50Builder plus overage, $0.038 a call | $1,729Growth plus overage, $0.035 a call |
| Cekura | $50Pay as you go, $0.05 a call | $500$0.05 a call | $2,500$0.05 a call |
| Coval | $100Starter, $0.10 a call | $500Growth, $0.05 a call | $2,500 to $6,500$0.05 to $0.13 a call |
| Bluejay | $500Growth, $0.50 a call | $1,000Scale, $0.10 a call | about $6,100$0.12 a call, derived |
| Roark | $500Team, $0.50 a call | $3,720Team, $0.37 a call | $18,600Team, $0.37 a call |
| Retell AI QA add-on | $290$0.29 a call | $2,990$0.30 a call | $14,990$0.30 a call |
| Hamming, the vendor this page compares | Contact sales only | Contact sales only | Contact sales only |
List prices read on from each vendor's pricing page.
Signal's price includes the copilot, simulated tests, the API and the MCP server, all paid from its credits. The other figures cover monitoring only.
How each figure was built
- Signal
- Computed from Signal's plans: the smallest plan with enough credits for the volume at 3 minutes a call, at its monthly or annual price.
- Tuner
- About 5 credits a call (from "5,000 credits (~1,000 calls)"). 10,000 calls is 50,000 credits, $39 plus 45,000 × $0.0075. 50,000 calls is 250,000 credits, $399 plus 190,000 × $0.007. Tuner shows no annual discount. Tuner pricing
- Cekura
- "$0.05 per monitored call", flat, so length does not matter. Cekura pricing
- Coval
- Growth $500 plus 40,000 calls over. The page prints the overage as "$0.05/monitoring min" while including calls, so the unit is ambiguous: $2,000 over if per call, $6,000 over if per minute. Coval pricing
- Bluejay
- 150,000 monitoring minutes against 34,000 included, 116,000 over at 1.5x of the implied $1,000 / 34,000 a minute. The implied rate is derived, not printed. Bluejay pricing
- Roark
- 5 metrics at $0.02 each plus $0.024 transcription is $0.124 a minute. At 1,000 calls usage is $372, so the $500 minimum applies. At 50,000 calls Roark would negotiate an Enterprise deal (floor "$4,000+"). Roark pricing
- Retell AI QA add-on
- "$0.10/min" after "First 100 minutes free", assuming the free minutes renew monthly (the page does not say). It sits on top of Retell's voice fees. Retell pricing
- Hamming
- Hamming prints no price. Its own blog estimates "~$2-5K/month for most teams", a vendor estimate and not a price. Hamming pricing Hamming blog estimate
How Hamming works
Hamming (YC S24) is built around testing. Automated Testing writes hundreds of scenarios from your agent’s prompt and runs them as simulated calls with accents, background noise, keypad input and phone menu trees. Red Teaming covers prompt injection, jailbreaks and PII leakage, and each finding becomes a failing test you can run again.
Production Monitoring runs health checks around the clock. Calls are scored by more than 50 built-in metrics in three groups: conversational quality, expected outcomes and compliance guardrails. Calls get outcome tags. Traces carry OpenTelemetry ids across speech to text, the model and text to speech, and alerts go to Slack, email or a webhook.
To bring Retell calls in, you send Retell’s call_ended payload to Hamming’s
call-log endpoint, through a webhook you wire up yourself or a relay. Their
public material does not describe a backfill of past calls.
Their best idea, in their words: “Every failure becomes a test scenario.” A failed production call seeds a synthetic scenario that runs on every release.
Hamming’s docs sit behind an access code and prices are quote only, so this page is thinner than the others.
Where Signal differs
What to change, not whether it is healthy. Hamming’s monitoring answers “is the agent healthy right now”. Signal answers “what should I change”, by reading your flow and placing each issue on the step, tool or transition where it happens, with a cause.
Nothing to write first. You approve a one-page brief drafted from your configuration. There are no assertions or scorers to choose before you know what is going wrong.
How sure it is. Each cause says how it is known: measured, visible in the trace, inferred by a model, or not established. The board prints “cause not established” rather than a guess.
Proof on production. When a new version ships, Signal compares before and after once it has taken calls for a grace period, and says whether the difference is real or that there are not enough calls yet.
Where Hamming is stronger. Simulation at scale, red teaming, languages, compliance (SOC 2 Type II, HIPAA BAA), latency tracing across the voice stack, and a mature path from production failure to regression test. If you are in healthcare, Hamming is built for you and Signal is not yet.
What it costs
Hamming does not publish prices. Their FAQ says pricing is volume based (tests plus monitored calls), not per seat, with Startup, Agency and Enterprise tiers, all through a sales call, and no self-serve trial. We could not find a reliable public figure, so the price table on this page shows them as quote only.
Signal charges a flat monthly plan with one balance of credits: each minute of a call costs a credit once it has started, and tests and the copilot draw on the same balance. Adding a check does not change the bill, and there is no charge per metric. There are no overage charges either: calls past the balance are stored, and analysed when the month resets or after an upgrade.
Using both
- Signal reads production and names the issue: the step, the cause, the calls behind it.
- Those calls are the ones worth turning into Hamming regression tests, so your suite covers what actually breaks in production.
- Hamming runs them on every release, alongside its red-team and load tests.
- After release, Signal checks production: did the issue shrink, and did anything else get worse.
Signal reads Retell over the API, so it does not interfere with the webhook or relay you set up for Hamming.
Checked on 22 September 2026 against Hamming's public pages.hamming.ai